Process to produce polycarbamate using a gradient feed of urea

ABSTRACT

A process to produce polycarbamate comprising providing urea in liquid form; and adding the urea in liquid form to a polyol in a reduced gradient profile to form polycarbamate product is provided. Also provided are: (a) a reaction product of the process and (b) an apparatus for operating the process.

FIELD OF INVENTION

The instant invention relates to a process to produce polycarbamate, areaction product thereof and an apparatus for conducting the process.

BACKGROUND OF THE INVENTION

Polyurethane is a polymer composed of a chain of organic units withcarbamate linkages. Polyurethanes may be produced using isocyanate as astarting material. However, trace amounts of residual isocyanates raisehealth and safety concerns. As an alternative, polyurethanes have beenproduced using polyols and methyl carbamate as the starting materials.Methyl carbamate, however, also gives rise to health and safetyconcerns. There remains a need for alternative polyurethane productionmethods which provide polyurethanes useful in a variety of applicationswhile minimizing health and safety concerns.

SUMMARY OF THE INVENTION

The instant invention is a process to produce polycarbamate, a reactionproduct thereof and an apparatus for conducting the process.

In one embodiment, the instant invention provides a process to producepolycarbamate comprising: providing urea in liquid form; adding the ureain liquid form to a polyol in a reduced gradient profile to formpolycarbamate product.

BRIEF DESCRIPTION OF THE DRAWINGS

For the purpose of illustrating the invention, there is shown in thedrawings a form that is exemplary; it being understood, however, thatthis invention is not limited to the precise arrangements andinstrumentalities shown.

FIG. 1 is a block flow diagram illustrating an embodiment of anapparatus for operating the inventive process; and

FIG. 2 is a graph illustrating the mass of urea in the reactor as afunction of time.

DETAILED DESCRIPTION OF THE INVENTION

The instant invention is a process to produce polycarbamate, a reactionproduct thereof and an apparatus for conducting the process.

The process to produce polycarbamates according to the present inventioncomprises providing urea in liquid form; and adding the urea in liquidform to a polyol in a reduced gradient profile to form polycarbamateproduct.

In an alternative embodiment, the instant invention further provides areaction product produced by any embodiment of the inventive processdescribed herein.

In yet another embodiment, the instant invention provides an apparatusfor operating any embodiment of the inventive process described herein.

Urea

The liquid form of the urea (or “liquid urea”) may be achieved in anyacceptable manner. For example, the urea may be dissolved in a firstsolvent. Alternatively, the urea may be melted. In yet anotheralternative, the urea may be suspended in a clathrate. A urea clathratemay also be known as a urea inclusion compound and may have thestructure as described in “Supramolecular Chemistry” John Wiley & Sons,Jonathan w. Steed, Jerry L. Atwood, pp. 393-398 and Harris, K. D. M.,“Fundamental and Applied Aspects of Urea and Thiourea InclusionCompounds”, Supramol. Chem. 2007, 19, 47-53.

The liquid form of the urea may alternatively be present in acombination of liquid forms.

In a particular embodiment, the urea is dissolved in water. In anotherembodiment, the urea may be dissolved in a mixture of two or more firstsolvents. Such first solvents include organic solvents. In analternative embodiment, the urea is dissolved in one or more solventsselected from water and organic alcohols. In one embodiment, urea ispartially soluble in the solvent or mixture of solvents. In yet anotherembodiment, urea is fully soluble in the solvent or mixture of solvents.

Polyol

As used herein, the term “polyol” means an organic molecule having atleast 2-OH functionalities. As used herein, the term “polyester polyol”means a subclass of polyol that is an organic molecule having at least 2alcohol (—OH) groups and at least one carboxylic ester (CO₂—C)functionality. The term “alkyd” means a subclass of polyester polyolthat is a fatty acid-modified polyester polyol wherein at least onecarboxylic ester functionality is preferably derived from anesterification reaction between an alcoholic —OH of the polyol and acarboxyl of a (C₈-C₆₀) fatty acid. The polyol may be any polyol; forexample, the polyol may be selected from the group consisting ofacrylic, styrene-acrylic, styrene-butadiene, saturated polyester,polyalkylene polyols, urethane, alkyd, polyether or polycarbonate. Inone exemplary embodiment, the polyol component comprises hydroxyethylacrylate. In another exemplary embodiment, the polyol componentcomprises hydroxyethyl methacrylate.

The reaction mixture may comprise from 10 to 100 percent by weight ofpolyol; for example, from 30 to 70 percent by weight of polyol. In oneembodiment, the polyol has a functional structure of a 1,2-diol,1,3-diol, or combinations thereof.

The polyol can be non-cyclic, straight or branched; cyclic andnonaromatic; cyclic and aromatic, or a combination thereof. In someembodiments the polyol comprises one or more non-cyclic, straight orbranched polyols. For example, the polyol may consist essentially of oneor more non-cyclic, straight or branched polyols.

In one embodiment, the polyol consists essentially of carbon, hydrogen,and oxygen atoms. In another embodiment, the polyol consists of primaryhydroxyl groups. In yet another embodiment, the hydroxyl groups are inthe 1,2 and/or 1,3 configuration. Exemplary polyol structures are shownbelow for illustrative purposes.

Polyol useful in embodiments of the inventive process include oligomersor polymers derived from hydroxy-containing acrylic monomeric units.Suitable monomers may be, but are not limited to, hydroxyethyl acrylate,hydroxypropyl acrylate, hydroxybutyl acrylate, hydroxydodecyl acrylate,hydroxyethyl methacrylate, hydroxypropyl methacrylate, hydroxybutylmethacrylate, hydroxydodecyl methacrylate, hydroxybutyl vinyl ether,diethylene glycol vinyl ether and a combinations thereof. The polyoluseful in embodiments may be prepared by reacting at least onehydroxyl-containing monomer with one or more monomers. Suitable monomersmay be, but are not limited to, vinyl monomers such as styrene, vinylether, such as ethyl vinyl ether, butyl vinyl ether, cyclohexyl vinylether, ester of unsaturated carbonic acid and dicarbonic acid, such asmethyl acrylate, methyl methacrylate, ethyl acrylate, ethylmethacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, dodecylacrylate, dodecyl methacrylate, dimethyl maleate and a mixture thereof.

Polyols useful in certain embodiments of the inventive process includepolyether polyols and polyester polyols. Suitable polyols include, forexample, ethylene glycol, diethylene glycol, neopentyl glycol,1,4-butanediol, 1,6-hexanediol, glycerol, pentaerythritol, sorbitol andmannitol. Suitable glycols thus include ethylene glycol, propyleneglycol, diethylene glycol, triethylene glycol, tetraethylene glycol,pentaethylene glycol, hexaethylene glycol, heptaethylene glycol,octaethylene glycol, nonaethylene glycol, decaethylene glycol, neopentylglycol, glycerol, 1,3-propanediol, 2,4-dimethyl-2-ethyl-hexane-1,3-diol,2,2-dimethyl-1,2-propanediol, 2-ethyl-2-butyl-1,3-propanediol,2-ethyl-2-isobutyl-1,3-propanediol, 1,3-butanediol, 1,4-butanediol,1,5-pentanediol, 1,6-hexanediol, 2,2,4-tetramethyl-1,6-hexanediol,thiodiethanol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol,1,4-cyclohexanedimethanol, 2,2,4-trimethyl-1,3-pentanediol,2,2,4-tetramethyl-1,3-cyclobutanediol, p-xylenediol, hydroxypivalylhydroxypivalate, 1,10-decanediol, hydrogenated bisphenol A,trimethylolpropane, trimethylolethane, pentaerythritol, erythritol,threitol, dipentaerythritol, sorbitol, mannitol, glycerine,dimethylolpropionic acid, and the like.

Polycarboxylic acids useful in the invention may include, but are notlimited to, phthalic anhydride or acid, maleic anhydride or acid,fumaric acid, isophthalic acid, succinic anhydride or acid, adipic acid,azeleic acid, and sebacic acid, terephthalic acid, tetrachlorophthalicanhydride, tetrahydrophthalic anhydride, dodecanedioic acid, sebacicacid, azelaic acid, 1,4-cyclohexanedicarboxylic acid,1,3-cyclohexanedicarboxylic acid, 2,6-naphthalenedicarboxylic acid,glutaric acid, trimellitic anhydride or acid, citric acid, pyromelliticdianhydride or acid, trimesic acid, sodium sulfoisophthalic acid, aswell as from anhydrides of such acids, and esters thereof, where theyexist. Optionally monocarboxylic acids may be employed including, butnot limited to, benzoic acid. The reaction mixture for producing alkydsincludes one or more aliphatic or aromatic polycarboxylic acids,esterified polymerization products thereof, and combinations thereof. Asused herein, the term “polycarboxylic acid” includes both polycarboxylicacids and anhydrides thereof. Examples of suitable polycarboxylic acidsfor use in the present invention include phthalic acid, isophthalicacid, terephthalic acid, tetrahydrophthalic acid, naphthalenedicarboxylic acid, and anhydrides and combinations thereof.

Addition Step

In a certain embodiment of the process, the addition of the urea inliquid form to the polyol is conducted in the presence of a catalyst.Suitable catalysts for use in this process include, but are not limitedto, organo-tin compounds. The use of this type of catalyst is well knownin the art. Examples of catalysts useful in the present inventioninclude, but are not limited to, dibutyltin diacetate, and dibutyltinoxide. In a particular embodiment, the catalyst is used in an amountfrom 0.1% to 1.0 wt % based on polyol weight. All individual values andsubranges from 0.1 to 1.0 wt % are included herein and disclosed herein;for example, the catalyst amount may range from a lower limit of 0.1,0.2, 0.4, 0.6 or 0.8 wt % based on polyol weight to an upper limit of0.15, 0.3, 0.5, 0.7, 0.9 or 1.0 wt % based on polyol weight. Forexample, the catalyst amount, in certain embodiments, may be from 0.1 to1.0 wt % based on polyol weight, or in the alternative, from 0.5 to 1.0wt % based on polyol weight, or in the alternative, from 0.1 to 0.6 wt %based on polyol weight.

In one embodiment of the first process, the polyol is complete polyol inthe absence of any solvent. In an alternative embodiment of the firstprocess, the polyol is dissolved in a second solvent prior to the addingthe liquid urea to the dissolved polyol. The second solvent may be anysolvent or mixture of solvents in which the polyol is soluble orpartially soluble. In certain embodiments, the first and second solventsform a heterogeneous azeotrope allowing removal of the first solvent bydecantation or other means. In certain embodiments, removal of the firstsolvent from a heterogeneous azeotrope permits concurrent removal ofcertain by-products, such as ammonia, which are soluble in the firstsolvent. In yet an alternative embodiment, the first and second solventsform a heterogeneous azeotrope allowing removal of the first solvent andfurther wherein the second solvent is returned to the reactor.

In certain embodiments, the process achieves at least a 50% conversionof hydroxyl groups of the polyol. All individual values and subrangesfrom at least 50% conversion are included herein and disclosed herein;for example, the hydroxyl conversion may range from a lower limit of50%, or in the alternative, the hydroxyl conversion may range from alower limit of 55%, or in the alternative, the hydroxyl conversion mayrange from a lower limit of 60%, or in the alternative, the hydroxylconversion may range from a lower limit of 65%, or in the alternative,the hydroxyl conversion may range from a lower limit of 70%, or in thealternative, the hydroxyl conversion may range from a lower limit of 75%or in the alternative, the hydroxyl conversion may range from a lowerlimit of 80%, or in the alternative, the hydroxyl conversion may rangefrom a lower limit of 85%.

Gradient Profile of Urea Addition

In embodiments of the inventive process, the liquid urea is added to thepolyol with a gradient feed rate. As used herein, gradient feed ratemeans that the feed rate of the urea changes in a nonlinear manner as afunction of time. The consumption of the hydroxyl groups of the polyolin the reaction with urea is a second order reaction and the hydroxylconcentration decreases exponentially with reaction time. The gradientprofile adjusts the liquid urea feeding rate according to theconsumption of hydroxyl functionality in a manner to avoid or minimizethe accumulation of unreacted urea in the reaction system. In yetanother embodiment, the gradient profile results in reducing theformation of impurities, and particularly impurities arising from thefollowing reactions:

In an alternative embodiment, the instant invention provides a process,reaction product thereof and an apparatus for conducting the process inwhich urea in liquid form is used, in accordance with any of thepreceding embodiments, except that the urea feeding rate is dynamicallyupdated according to the following:

C_(u) ≈ constant  during  feeding  time;${\frac{{F_{u}(t)} \cdot \rho_{soln} \cdot {{{Conc}({urea})}/M_{urea}}}{V_{r}} = {{\alpha \cdot C_{OH}} = {{\alpha \cdot C_{OH}^{0}}{\mathbb{e}}^{{- {kC}_{u}}t}\mspace{14mu}{and}}}}\mspace{14mu}$∫₀^(t_(f))F_(u)(t) 𝕕t = V_(u),wherein t_(f)=urea solution feeding time; C_(u)=pseudo-steady stateconcentration of urea in reactor during feeding, C_(u)≦ solubility ofurea in the reaction system; F_(u)(t)=urea solution feeding rate;ρ_(soln)=urea solution density; M_(urea)=urea molecular weight;Conc(urea)=concentration of urea in the feeding stream; C_(OH)=hydroxylmolar concentration; C_(OH) ⁰=initial hydroxyl molar concentration;k=reaction rate coefficient of the desired reaction; α=proportionalcoefficient of OH concentration and feeding rate; V_(r)=total reactantmixture volume in reactor and V_(u)=total urea solution volume.

In an alternative embodiment, the instant invention provides a process,reaction product thereof and an apparatus for conducting the process, inaccordance with any of the preceding embodiments, except that thegradient feeding rate of the urea is calculated based on two conditions:(1) the urea concentration is assumed to be at pseudo-steady state,i.e., the difference of urea concentration change caused by the feedingand the consumption by reaction is a constant; and (2) the integral ofthe urea feeding rate over a specified feeding time equals to the totalvolume of urea added to the reactor. The first condition may beexpressed by the following equation: C_(u)≈constant during feeding time;and the second condition may be expressed as follows:∫₀ ^(t) ^(f) F _(u)(t)dt=V _(u)

In an alternative embodiment, the instant invention provides a process,reaction product thereof and an apparatus for conducting the process, inaccordance with any of the preceding embodiments, except that thedetermination of the optimal urea feeding rate is based on a kineticmodel calculation of OH concentration.

In an alternative embodiment, the instant invention provides a process,reaction product thereof and an apparatus for conducting the process, inaccordance with any of the preceding embodiments, except that thekinetic modeling is based upon

${F_{u}(t)} = {\frac{{\alpha \cdot C_{OH}^{0}}{{\mathbb{e}}^{{- {kC}_{u}}t} \cdot V_{r} \cdot M_{urea}}}{\rho_{soln} \cdot {{conc}({urea})}}.}$

As used in the foregoing equations: t_(f)=urea solution feeding time;C_(u)=concentration of urea in reactor during feeding, C_(u)≦ solubilityof urea in the reaction system; F_(u)(t)=urea solution feeding rate;ρ_(soln)=urea solution density; M_(urea)=urea molecular weight;Conc(urea)=concentration of urea in the feeding stream; C_(OH)=hydroxylmolar concentration; C_(OH) ⁰=initial hydroxyl molar concentration;k=reaction rate coefficient of the desired reaction; α=proportionalcoefficient of OH concentration and feeding rate; V_(r)=total reactantmixture volume in reactor and V_(u)=total urea solution volume.

In an alternative embodiment, the instant invention provides a process,reaction product thereof and an apparatus for conducting the process, inaccordance with any of the preceding embodiments, except that thedetermination of the optimal urea feeding rate is based on measurementof OH concentration in the reactor. The OH concentration measurement maybe accomplished by in situ reactor measurement or ex situ analysis of asample removed from the reactor. OH concentration may be determinedusing any appropriate analytical technique, including for example, OHnumber titration, nuclear magnetic resonance (NMR), infraredspectroscopy (IR), near infrared spectroscopy (NIR) or Ramanspectroscopy.

The urea gradient feeding process can be carried out in either acontinuous or a discontinuous feeding approach.

An exemplary apparatus useful in embodiments of the present invention isshown in FIG. 1. Liquid urea feed into the reactor is controlled by aFeeding Controller. A Reactor Measurement System may be configured inany manner so as to obtain information (for example, the level of —OH,reactant mixture volume, etc. . . . ) in the reactor. For example, theReactor Measurement System may include probes for measuring —OH in thereactor. Alternatively, the Reactor Measurement System may involve theremoval of samples from the reactor for —OH concentration measurementexternal to the reactor. The level of —OH determined by the ReactorMeasurement System is used in the equations described herein tocalculate the rate of urea to be fed into the reactor. The feeding rateof urea can also be influenced by other process parameters, for example,the impurities levels in reactor. Such calculations may occur internallyor externally of the Feeding Controller. If the calculations areconducted externally to the Feeding Controller, the amount of urea to befed into the reactor is supplied to the Feeding Controller.

In an alternative embodiment, the instant invention provides a process,reaction product thereof and an apparatus for conducting the process, inaccordance with any of the preceding embodiments, except that the 100%solids polycarbamate product comprises less than or equal to 0.1 wt %cyanuric acid. All individual values and subranges less than or equal to0.1 wt % is included herein and disclosed herein; for example, the levelof cyanuric acid may be from an upper limit of 0.1 wt %, or in thealternative, the level of cyanuric acid may be from an upper limit of0.08 wt %, or in the alternative, the level of cyanuric acid may be froman upper limit of 0.07 wt %, or in the alternative, the level ofcyanuric acid may be from an upper limit of 0.06 wt %.

In an alternative embodiment, the instant invention provides a process,reaction product thereof and an apparatus for conducting the process, inaccordance with any of the preceding embodiments, except that the 100%solids polycarbamate product comprises less than or equal to 0.4 wt %biuret. All individual values and subranges less than or equal to 0.4 wt% is included herein and disclosed herein; for example, the level ofbiuret may be from an upper limit of 0.4 wt %, or in the alternative,the level of biuret may be from an upper limit of 0.35 wt %, or in thealternative, the level of biuret may be from an upper limit of 0.3 wt %,or in the alternative, the level of biuret may be from an upper limit of0.25 wt %, or in the alternative, the level of biuret may be from anupper limit of 0.2 wt %.

In an alternative embodiment, the instant invention provides a process,reaction product thereof and an apparatus for conducting the process, inaccordance with any of the preceding embodiments, except that the 100%solids polycarbamate product comprises less than or equal to 1.5 wt %polyallophanate. All individual values and subranges less than or equalto 1.5 wt % is included herein and disclosed herein, for example, thelevel of polyallophanate may be from an upper limit of 1.4 wt %, or inthe alternative, the level of polyallophanate may be from an upper limitof 1.3 wt %, or in the alternative, the level of polyallophanate may befrom an upper limit of 1.2 wt %, or in the alternative, the level ofpolyallophanate may be from an upper limit of 1.15 wt %.

In an alternative embodiment, the instant invention provides a process,reaction product thereof and an apparatus for conducting the process, inaccordance with any of the preceding embodiments, except that the 100%solids polycarbamate product comprises less than or equal to 0.5 wt %unreacted urea. All individual values and subranges less than or equalto 0.5 wt % is included herein and disclosed herein; for example, thelevel of unreacted urea may be from an upper limit of 0.5 wt %, or inthe alternative, the level of unreacted urea may be from an upper limitof 0.36 wt %, or in the alternative, the level of unreacted urea may befrom an upper limit of 0.2 wt %, or in the alternative, the level ofunreacted urea may be from an upper limit of 0.15 wt %.

EXAMPLES

The following examples illustrate the present invention but are notintended to limit the scope of the invention.

Comparative Example-1

A 50-L jacketed reactor was used for this reaction. The jacket fluid washeated by a heater equipped with a circulation pump. A thermocouple wasused to monitor the reactor inner temperature. A nitrogen sparging tubewas fed through the reactor top adaptors. The reactor was agitated usingtwo Teflon agitators driven by a motor through the center adaptor on thereactor cover. A water-cooled overhead condenser with a 1-L receiver wasinstalled to collect overhead liquid. The non-condensable gas wentthrough a bubbler filled with mineral oil and then entered a 4-Lscrubber filled with water.

18.2 kg PARALOID AU-608X polyol (commercially available from The DowChemical Company) was heated to 60° C. and then pumped into the reactor,which consisted of 58 wt % dry polyol and 42 wt % solvent (xylenes). Theagitator was started and set at 50 rpm. 3.1 kg xylene solvent was pumpedinto the reactor to lower the mixture viscosity. 111.2 g (98% pure)dibutyltin oxide was added to the reactor. The jacket fluid heater wasset at 158° C. The nitrogen sparging rate was started and the flow ratewas set at 0.6 L/min. The stirring rate was increased to 180 rpm.

953.1 g (98% pure) urea was dissolved in 883.3 g deionized water to formaqueous solution. The urea solution was transferred to a 2-L reactorequipped with a pump. The 2-L reactor was agitated at 30 rpm and inertedusing nitrogen. When the 50-L reactor temperature reached 140° C., theurea solution pump was started and the flow rate was set at 20 ml/min.The reaction timer was started. The addition of urea solution at 20ml/min lasted for 31 minutes and the pump rate was adjusted to 2 ml/minto feed the balance of the urea solution. During the urea solutionfeeding step, the azeotrope of water and xylene was collected in theoverhead receiver. Xylene was separated and recycled. After ureasolution feeding was complete, the reaction was carried out until thetotal batch time reached 30 hours. The reactor heater set temperaturewas set at 70° C. and the stirring rate was set at 50 rpm to cool downthe reactor. The reactor was shut down when the reactor temperature waslower than 60° C. The reactor was drained and the resulting product wascloudy with a Gardner level between 2 and 3. 19.8 kg total reactionproduct was collected. Table 1 below provides OH conversion andby-product and unreacted urea information for Comparative Example 1.Target product selectivity is the percentage of urea reacted to formpolycarbamate.

TABLE 1 OH conversion 72.2% Target product selectivity 79.2% Sideproducts and residues in 100% solids product Biuret 0.56 wt % Cyanuricacid 0.03 wt % Polyallophanate 0.62 wt % Unreacted urea 0.44 wt % Sideproducts and residues in final product (including solvent) Biuret 0.32wt % Cyanuric acid 0.02 wt % Polyallophanate 0.35 wt % Unreacted urea0.25 wt %

Inventive Example 1

A 50-L jacketed reactor was used for this reaction. The jacket fluid washeated by a heater equipped with a circulation pump. A thermocouple wasused to monitor the reactor inner temperature. A nitrogen sparging tubewas fed through the reactor top adaptors. The reactor was agitated usingtwo Teflon agitators driven by a motor through the center adaptor on thereactor cover. A water-cooled overhead condenser with a 1-L receiver wasinstalled to collect overhead liquid. The non-condensable gas wentthrough a bubbler filled with mineral oil and then entered a 4-Lscrubber filled with water.

18.1 kg PARALOID AU-608X polyol was heated to 60° C. and then pumpedinto the reactor, which consisted of 58 wt % dry polyol and 42 wt %solvent (xylenes). The agitator was started and set at 50 rpm. 3.3 kgxylene solvent was pumped into the reactor to lower the mixtureviscosity. 110.8 g (98% pure) dibutyltin oxide was added to the reactor.The heater was set at 158° C. The nitrogen sparging rate was started andthe flow rate was set at 0.6 L/min. The stirring rate was increased to180 rpm.

935.9 g (98% pure) urea was dissolved in 1143.9 g deionized water toform aqueous solution. The urea solution was transferred to a 2-Lreactor equipped with a pump. The 2-L reactor was agitated at 30 rpm andinerted using nitrogen. When the 50-L reactor temperature reached 140°C., the urea solution pump was started and the reaction timer wasstarted. The urea solution was fed into the reactor in a gradient mannerover 10 hours. The feeding rates over the course of the reaction were asshown in Table 2.

TABLE 2 Urea Solution feeding rate Time (hr) (ml/min) 1 4.17 2 3.83 33.51 4 3.23 5 2.96 6 2.72 7 2.49 8 2.29 9 2.10 10 1.93

During urea solution feeding step, the azeotrope of water and xylene wascollected in the overhead receiver. Xylene was separated and recycled.After urea solution feeding was complete, the reaction was carried outuntil the total batch time reached 30 hours. The reactor heater settemperature was set at 70° C. and the stirring rate was set at 50 rpm tocool down the reactor. The reactor was shut down when the reactortemperature was lower than 60° C. The reactor was drained and theproduct was clear with a Gardner level of less than or equal to 1. 18.7kg total reaction product was collected. Table 3 provides the —OHconversion, unreacted OH and by-product levels.

TABLE 3 OH conversion 82.4% Target product selectivity 86.9% Sideproducts and residues in 100% solids product Biuret 0.18 wt % Cyanuricacid 0.05 wt % Polyallophanate 1.00 wt % Unreacted urea 0.10 wt % Sideproducts and residues in final product (including solvent) Biuret 0.11wt % Cyanuric acid 0.03 wt % Polyallophanate 0.60 wt % Residual urea0.06 wt %

In Comparative Example 1 the urea solution was fed using two rates (20ml/min and 2 ml/min). In Inventive Example 1 the urea solution was fedusing a gradient feeding rate as shown above. Comparative Example 1exhibited an OH conversion of 72%. The low polycarbamate functionalitycontent in the product provided insufficient crosslinking capability foruse in coating applications. The product from Comparative Example 1 alsoexhibited a heavy color and higher unreacted urea content. Furthermore,due to the higher level of by-product formation, the selectivity of thetarget reaction (i.e., formation of polycarbamate) was only 79.2%.

Inventive Example 1 exhibited a higher OH conversion, 82.4%. Theselectivity for the target reaction was also much higher than that ofComparative Example 1, namely 86.9%. The biuret level and unreacted ureaare both substantially lower than achieved by Comparative Example 1.

Exemplary Calculations

1. Pseudo-Steady State Urea Concentration

The urea steady state concentration determination is a trial-and-errorprocedure. A reaction is run with a urea concentration determined eitherfrom similar condition batches or from an empirical estimation in thecalculation of urea feeding rate. During the reaction, the actual ureaconcentration were determined and the model corrected for future batchreactions. In the calculation, the first assumption is that the ureaconcentration (C_(u)) is relatively stable. FIG. 2 shows the actual ureain a 1-L batch reaction of urea and polyol determined using NMR. Theurea was fed in a gradient manner over a period of 8 hours. As seen inFIG. 2, the urea content is relatively stable during most of the feedingperiod, thereby verifying the steady state assumption. The calculatedaverage urea concentration during feeding is 0.143 mol/L, which was usedas C_(u) for the gradient feeding rates calculation. One of ordinaryskill in the art would understand that the steady state ureaconcentration will vary based upon the reactants used and reactionconditions. One of ordinary skill in the art would further understandthat the allowed steady state urea concentration will depend on theallowed impurities levels in the final product.

2. Gradient Feeding Calculation

The parameter values in Table 4 were used for the gradient feeding ratein Inventive Example 1.

TABLE 4 t_(f) 10 hr Total urea feeding time for Inventive Example 1C_(OH) ⁰  0.91 mol/L Initial OH concentration for Inventive Example 1 k0.6 L/ Target reaction kinetic parameter fit from (mol · hr) model forPARALOID AU-608X C_(u) 0.143 mol/L Urea concentration (pseudo-steadystate) for Inventive Example 1 V_(r) 25 L Reactant volume for InventiveExample 1 M_(urea) 60.06 g/mol Urea molecular weight ρ_(soln) 1.15 g/mlUrea solution density for Inventive Example 1 Conc 45.0% Urea solutionconcentration for Inventive (urea) Example 1

These parameter values were used in

${F_{u}(t)} = \frac{{\alpha \cdot C_{OH}^{0}}{{\mathbb{e}}^{{- {kC}_{u}}t} \cdot V_{r} \cdot M_{urea}}}{\rho_{soln} \cdot {{conc}({urea})}}$and${\int_{0}^{t_{f}}{\frac{{\alpha \cdot C_{OH}^{0}}{{\mathbb{e}}^{{- {kC}_{u}}t} \cdot V_{r} \cdot M_{urea}}}{\rho_{soln} \cdot {{conc}({urea})}}{\mathbb{d}t}}} = V_{u}$

V_(u) was calculated to be 1754 ml. The coefficient α was determinedusing:

${{\alpha \cdot \frac{1}{- {kC}_{u}}}{\mathbb{e}}^{{- {kC}_{u}}t}}|_{0}^{t_{f}}{= \frac{V_{u} \cdot \rho_{soln} \cdot {{conc}({urea})}}{C_{OH}^{0} \cdot V_{r} \cdot M_{urea}}}$

In Inventive Example 1, α=0.094769, and the feeding rates in Table 2were calculated.

Test Methods

Test methods include the following:

OH Number Titration

OH number is the magnitude of the hydroxyl number for a polyol asexpressed in terms of milligrams potassium hydroxide per gram of polyol(mg KOH/g polyol). Hydroxyl number (OH #) indicates the concentration ofhydroxyl moieties in a composition of polymers, particularly polyols.The hydroxyl number for a sample of polymers is determined by firsttitrating for the acid groups to obtain an acid number (mg KOH/g polyol)and secondly, acetylation with pyridine and acetic anhydride in whichthe result is obtained as a difference between two titrations withpotassium hydroxide solution, one titration with a blank for referenceand one titration with the sample. A hydroxyl number is the weight ofpotassium hydroxide in milligrams that will neutralize the aceticanhydride capable of combining by acetylation with one gram of a polyolplus the acid number from the acid titration in terms of the weight ofpotassium hydroxide in milligrams that will neutralize the acid groupsin the polyol. A higher hydroxyl number indicates a higher concentrationof hydroxyl moieties within a composition. A description of how todetermine a hydroxyl number for a composition is well-known in the art,for example in Woods, G., The ICI Polyurethanes Book, 2^(nd) ed. (ICIPolyurethanes, Netherlands, 1990).

Gardner color: was measured according to ASTM D1544 “Standard TestMethod for Color of Transparent Liquids (Gardner Color Scale)” using aHunterLab colorimeter.

¹³C NMR: All samples were characterized by ¹³C NMR in solutions. For atypical sample preparation, 0.6 g dry material was dissolved in 2.5 mLDMSO-d₆ solvent at room temperature in a glass vial. The DMSO-d₆ solventcontains 0.015 M Cr(acac)₃ as a relaxation agent. The solution was thentransferred to a 10 mm NMR tube for characterization. Quantitativeinverse-gated ¹³C NMR experiments were performed on a Bruker Avance 400MHz (¹H frequency) NMR spectrometer equipped with a 10 mm DUAL C/Hcryoprobe. All experiments were carried out without sample spinning at25.0° C. Calibrated 90° pulse was applied in the inverse-gated pulsesequence. The relaxation delay between consecutive data acquisitions is5*T₁, where T₁ is the longest spin-lattice relaxation time of all nucleiin the measured system. The ¹³C NMR spectra were processed with a linebroadening of 1 Hz, and referenced to 39.5 ppm for the DMSO-d₆ resonancepeak.

Information that can be obtained from ¹³C NMR spectra includes thepercent of hydroxyl conversion, byproduct levels and solid content ofthe reaction product. The carbon next to a hydroxyl group has a chemicalshift change after the carbamylation reaction. The hydroxyl conversionwas calculated from the peak intensity ratio of the carbon after andbefore a carbamylation reaction. In a quantitative ¹³C NMR spectrum,each component of the measured system has a unique resonance peak, andits peak intensity is proportional to the molar concentration of thatspecies. The byproduct levels and solid content were calculated byintegrating the desired peaks. The molar concentration can be convertedto weight percentage if the molecular weights for all species are known.In calculating the solid content, any components other than knownsolvents are classified as solid.

The present invention may be embodied in other forms without departingfrom the spirit and the essential attributes thereof, and, accordingly,reference should be made to the appended claims, rather than to theforegoing specification, as indicating the scope of the invention.

The invention claimed is:
 1. An article comprising a polycarbamateobtained by a process comprising: providing urea in liquid form; addingthe urea in liquid form to a polyol in a reduced gradient profile toform polycarbamate product; wherein the polycarbamate product comprisesless than or equal to 0.1 wt % cyanuric acid.
 2. The article accordingto claim 1, wherein the urea in liquid form is urea dissolved in asolvent.
 3. The article according to claim 2, wherein the solvent iswater.
 4. The article according to claim 1, wherein the urea feedingrate is dynamically updated according to the following:C_(u) ≈ constant  during  feeding  time;${\frac{{F_{u}(t)} \cdot \rho_{soln} \cdot {{{Conc}({urea})}/M_{urea}}}{V_{r}} = {{\alpha \cdot C_{OH}} = {{\alpha \cdot C_{OH}^{0}}{\mathbb{e}}^{{- {kC}_{u}}t}\mspace{14mu}{and}}}}\mspace{14mu}$∫₀^(t_(f))F_(u)(t) 𝕕t = V_(u), wherein t_(f)=urea solution feeding time;C_(u)=concentration of urea in reactor during feeding, C_(u)≦ solubilityof urea in the reaction system; F_(u)(t)=urea solution feeding rate;ρ_(soln)=urea solution density; M_(urea)=urea molecular weight;Conc(urea)=concentration of urea in the feeding stream; C_(OH)=hydroxylmolar concentration; C_(OH) ⁰=initial hydroxyl molar concentration;k=reaction rate coefficient of the desired reaction; α=proportionalcoefficient of OH concentration and feeding rate; V_(r)=total reactantmixture volume in reactor and V_(u)=total urea solution volume.
 5. Thearticle according to claim 4, wherein hydroxyl molar concentration,C_(OH) is determined by measurement.
 6. The article according to claim5, wherein the adding the urea in liquid form to a polyol occurs in areactor and measurement is conducted in the reactor or by sampling fromthe reactor followed by analysis external to the reactor.
 7. The articleaccording to claim 4, wherein the reactor volume, Vr, is measured. 8.The article according to claim 4, wherein the hydroxyl molarconcentration, C_(OH) is determined by kinetic modeling.
 9. The articleaccording to claim 8, wherein the kinetic modeling is based upon${F_{u}(t)} = {\frac{{\alpha \cdot C_{OH}^{0}}{{\mathbb{e}}^{{- {kC}_{u}}t} \cdot V_{r} \cdot M_{urea}}}{\rho_{soln} \cdot {{conc}({urea})}}.}$